Method of rifling



April 9 I J. C. GARAND 2,397,544

METHOD OF RIFLING F iled Se t. 16, 1943 JWW JUHN E-GARAND,

Patented Apr. 2, 1946 UNITED STATES PATENT OFFICE METHOD OF RIFLING JohnC. Garand, Springfield, Mass. Application September 16, 1943,-Seriai-No.502, 699

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370O. G. 757) 1 Claim.

' The invention described herein may be manufactured and used by or forthe Government for governmental purposes, without the payment to me ofany royalty thereon.

This invention relates to a composite firearm barrel and to a method forforming the rifling in such barrel.

The conventional method of rifling a barrel for a firearm is to cuthelical grooves in the barrel by broaching or by a cutter in a rifiingmachine. Prior to machining a barrel blank the blank must be heattreated to obtain the desired physical properties of the finishedbarrel. Such heat treatment however generally does not improve themachlnability oi the blank. Machining operations on such a blank areextremely hard on the cutting tools thereby requiring frequentresharpening of such tools which adds materially to the cost offabrication of a barrel and to the time required to produce the riflingtherein. Further where difficult machining is encountered the surface ofthe bore of a barrel will invariably be rough. Such a rough surfaceinvites corrosion due to the diiliculty in keeping the bore clean.

In addition firearm manufacturers have found that steels of the typeknown as stainless steels which are highly corrosion resistant areespecially suitable for barrels for that reason. Steels of this classhowever have very poor machinability qualities which almost precludestheir use for barrels when such barrels are fabricated by conventionalmethods.

Accordingly, it is an object of this invention to provide an improvedfirearm barrel and an inexpensive and rapid method for fabricating afirearm barrel and particularly for forming the rifling in such barrel.

It is a particular object of this invention to provide a method ofrifiing a tube for a firearm barrel by the use of pressure to force thewalls of the barrel tube into the grooves of a master form.

The specific nature of the invention as well as other objects andadvantages thereof will clearly appear from a description of a preferredembodiment as shown in the accompanying drawing in which:

Fig. 1 is a perspective view of a portion of a barrel tube mounted on agrooved mandrel.

Fig. 2 is a cross-sectional view of the barrel tube and mandrel mountedbetween the rollers.

Fig. 3 is a cross-sectional view of the rifled tube assembled to abarrel jacket.

Fig. 4 is a partial longitudinal sectional view showing the barrel tubespun into the chamber of the barrel jacket.

Briefly, this invention comprises forcing a portion of the wall of abarrel tube into substantially helical grooves on a mandrel which isinserted within the barrel tube. The grooves on the mandrel, of course,conform to the twist of rifiing desired, The wall is forced into thesegrooves by rollers which bear against the outer surface of the tubedirectly opposite each groove as the tube and mandrel are drawn betweenthe rollers on a helix conforming to that of the grooves.

There is shown in Fig. 1 a section of a barrel tube I and a portion of amandrel 2 inserted within the barrel tube I. Four helical grooves 3 areexteriorly formed on mandrel 2. Any number of such grooves may beprovided, however, the number shown serving only for illustration. Thebarrel tube I with mandrel 2 inserted within tube I is then arranged sothat it may be drawn between four equally spaced oppositely disposedrollers 4 (Fig. 2). A suitable machine such as a planer (not shown) maybe utilized to pull the barrel tube and mandrel assembly between therollers 4, such machine to impart a helical motion to the barrel tubeand mandrel assembly as it is drawn between rollers 4 so that therollerswill depress the wall of the barrel tube. into grooves 3 inmandrel 2. It should be mentioned that the machine (not shown) must ofcourse produce the same helical lead as that of the grooves 3 in mandrel2.

It is desired to point out that the depth of the lands of a .30 caliberbarrel is only .004 of one inch. Lands of larger caliber rifles are ofcourse proportionately larger. It is thus readily apparcut that only acomparatively small amount of deforming is necessary to force the barreltube into grooves 3 of mandrel 2. The rollers 4 are preferably madeadjustable so that they may be moved nearer or farther away from thelongitudinal axis of the barrel jacket as may be desired. Rollers 4must, however, be set so that they will force the wall of barrel tube Ito completely fill the grooves 3. Each roller 4 is, of course, mounteddirectly over each groove 3. The barrel tube and mandrel assembly isthen drawn between the rollers 4 by the machine (not shown) employed.After the barrel tube has, been drawn through the rollers 4 mandrel 2 isremoved from barrel tube I as by an arbor press and the bore of. suchtube will then have integrally formed lands 5 as shown in Fig. 3. Slightdepressions 6 will be formed on the outside of barrel tube I where therollers 4 have come in contact with barrel tube I due to forcing thewall of the barrel tube I into grooves 3 of mandrel 2. It should bementioned the propelling gases.

The comparatively thin barrel tube I may then be shrunk, sweated orforced into a barrel jacket I (Figs. 3 and f1). Barrel jacket'lis ofcon- I I been metho'dewililikewfise'sbe exceptionally smooth andventional barrel. zconcfiguration whil'l'l'ha's bored out toreceive"ba'rrel tubel. Tlifibarrel jacket I is however provided with an enlargedlhe lands of the rifling formed in the barrel tube chamber 8. Whenbarrel tube I is forced into S barrel jacket I the portion of barreltube 1|: pros l jecting into ch'amber 8 is then spun or otherwise forcedinto intimate contact with the"-"walls of chamber 8. As lands 5 areofevery-slightudepth 7. as compared to the diameter of the bore theslight indentations 6 formed by rollers I are-like wise of very shallowdepth. However, the-.cross a: 3 section between the indentations 6 andthe topof lands 5 is still of the same cross section as of barrel tube land therefore-is of s'ufiic'i'ent' strength" I to withstand-any gas--pressure develol 'ed within the'bairel tube l': Additional support isprovided-' by barreljacket -1. Barrel-jacket 'I also "provid'es*-themeeessaryweight "to the' barrel assembly so necessary for thereduction'of recoil and ac ,scription that the barrel tube I may be madeof practically any material which can be deformed by rollers in themanner above described regardless of the toughness of machinability ofsuch material. It should also be appreciated that provided the tubingoriginally had a highly polished interior bore surface the lands formedby this highiypolisl'ied 'at'the eompietiomor forming.

in this manner are quickly and readily produced. Furtherrsuch landsproduced in this manner are quite inexpensively formed.

I claiin z Theimethodbf iorming a firearm-barrel con- "sisting of,placing a relatively thin metallic barrel tub'e ona mandrel which isprovided with ex- I terior substantiallyohelical grooves whichcorrespondinconfiguration to the lands desired in the firearm barrel,and then helically drawing said tube 'a ndmandrel between-a plurality 1of rollers each" bf wh-i'li -is arranged to overlie one of -"saidgrooves =whereby' rolling pressures are applied to said tube alonghelical paths wl ich directly -overlie said g rooves 'causing metal-ofsaidtube to flowintosaid-greovesik l JOHN C. GARAND;

